Transition from Associations to Links

[veprbl]

For example:

tutorial-developing-benchmarks/episodes/files/uchannelrho.cxx

Lines 68 to 71 in 48e604f

	// _ReconstructedChargedParticleAssociations_sim.index is the index into the
	// MCParticles collection; _..._rec.index is the index into ReconstructedChargedParticles.
	TTreeReaderArray<int> rec_id = {tree_reader, "_ReconstructedChargedParticleAssociations_rec.index"};
	TTreeReaderArray<int> sim_id = {tree_reader, "_ReconstructedChargedParticleAssociations_sim.index"};

cc eic/EICrecon#2822

[wdconinc]

The appropriate minimal conversion is to use, e.g.:

 // Get Links Between MCParticles and ReconstructedChargedParticles 
 TTreeReaderArray<unsigned int> recoAssoc(tree_reader, "_ReconstructedChargedParticleLinks_from.index");
 TTreeReaderArray<unsigned int> simuAssoc(tree_reader, "_ReconstructedChargedParticleLinks_to.index");

Note:

• use unsigned int for the index
• use _*Links_from.index and _*Links_to.index, but *Links.weight (without leading _)
• *Associations_rec becomes *Links_from
• *Associations_sim becomes *Links_to
• Comments are updated to refer to links instead of associations
• The use of *Assoc as the name of the TTreeReaderArray is acceptable.

This should be applied to all instances where associations are used, not just the one highlighted in this issue.